A person attending a "live" performance at an orchestral hall will hear many different sounds at the same time, for example, sounds originating from strings, wind or percussion instruments and voices. When listening to live music, the listener not only hears the individual sounds emanating from the musical instruments and/or singers, but also senses the specific locations where the instruments and/or singers are located. For example, the listener would hear the sounds generated by the french horns emanating from the right side of the stage where the french horn section is located, the sounds generated by the violins emanating from the center of the stage where the violins are located, and sounds generated by the tympani on the left where the percussion section is located. This aspect of determining the relative location of the instruments will be referred to herein as three-dimensional sound.
The concept of stereophony was introduced in an attempt to emulate in a listening room with a prerecorded or broadcast sound source the three-dimensional sound that would have been heard during a live performance of the same program.
In stereophony, a sound is typically recorded stereophonically by recording on separate, individual channels the sounds received by each of a plurality of microphones located at predetermined positions in the recording studio or concert hall. The sounds can be recorded on media such as a record, tape or compact disc. The recorded sound can subsequently be reproduced on a stereophonic or two-channel reproduction system such as a home stereo system. A home stereo system typically comprises a means for reading the sound information in the individual channels stored on the media, and generating electric signals representative of the information. The electronic signals are amplified and fed to electronic-to-acoustic transducers, such as loud-speakers, to generate the sound waves which the listener then hears.
It is desirable that the recorded sound reproduced on a stereo system sounds the same as the original sounds. In an attempt to achieve the best possible sound quality, stereo speakers are typically positioned a distance apart from one another. This is illustrated in FIG. 1. Instruments 11, 12 and 13 which, in this example produce music, are positioned at locations 10, 12 and 14 in a recording studio 16. Also situated in the recording studio 16 are two microphones M.sub.1 and M.sub.2 positioned at locations 18 and 20. The microphones M.sub.1 and M.sub.2 provide the means to record the sounds received at locations 18 and 20. Electrical signals representative of the sounds received through the microphones M.sub.1 and M.sub.2 are recorded on separate channels by sound recording and reproductions unit 22. In listening room 24, the sound recording and reproduction unit 22 is connected to speakers S.sub.1 and S.sub.2 at locations 26 and 28. Speakers S.sub.1 and S.sub.2 are positioned apart from one another in simulation of the separation of microphones M.sub.1 and M.sub.2. Speaker S.sub.1 reproduces the sounds recorded from microphone M.sub.1 and speaker S.sub.2 reproduces the sounds recorded from microphone M.sub.2. Thus, theoretically, the listener, positioned at location 30, would expect to hear the reproduced music from 12 with the same sensation if as being in the recording studio if the separation of speakers S.sub.1 and S.sub.2 is equal to that of microphones M.sub.1 and M.sub.2 , and the relative position of the ear 30 to the speakers S.sub.1 and S.sub.2 is equal to the relative position of the sound source 12 to M.sub.1 and M.sub.2. Each sound source 11, 12, and 13 has a different singular ear position 30 for ideal sound reproduction. In reality, however, the listener instead hears instruments 11, 12 and 13 originating simultaneously from both speakers. This produces artificial, distorted sounds because each of the original sounds, emanating from instruments 11, 12 and 13, originates from an individual distinct location 10, 12 and 14, respectively, dictated by the positions of the instruments, not from two separate locations as the listener perceives through the conventional stereophonic sound reproduction system. More specifically, the listener in the listening room hears a mixture of two distinct sources of sound from two speakers representative of the combination of microphones/speakers, M.sub.1 /S.sub.1 and M.sub.2 /S.sub.2 , which transmit the combination of sounds originating from each point source 11, 12 and 13.
Some improvement in the reduction of such distortion of reproduced sound can be achieved through the use of stereo headphones. Since the sounds out of the right and left speakers are fed directly and exclusively into the respective right and left ears of the listener, the mixing of sounds from the right and left speakers is substantially eliminated. However, the real situation is not completely emulated and the listener cannot discern the relative position of the individual sound sources.
For the accurate reproduction of sound, the listener should be able to hear three distinct sources of sounds, (i.e., the instruments) as well as the locations of the sound sources relative to one another (since that is what the listener would hear if he were listening to a "live" performance, that is, if the listener were physically located in front of sound producing instruments 11, 12 and 13).